As described in JPH7-100425 (“Patent literature 1”), drying furnaces for drying workpieces in the related art include a flat furnace that is substantially flat over a conveyance path from a workpiece carrying-in port to a workpiece carrying-out port and a mountain-shaped furnace that has an intermediate conveyance path located at a high position relative to a workpiece carrying-in port and a workpiece carrying-out port.
However, a flat furnace is substantially flat over the conveyance path and thus hot air in the drying furnace is likely to be released out of the furnace from the carrying-in port and the carrying-out port (a large heat loss from the carrying-in port and the carrying-out port), disadvantageously leading to low thermal efficiency in the drying furnace.
In a mountain-shaped furnace, an intermediate conveyance path is located at a high position relative to a workpiece carrying-in port and a workpiece carrying-out port and thus hot air in the drying furnace is less prone to being released out of the furnace from the carrying-in port and the carrying-out port. However, an inclined part needs to be provided between an intermediate part and the carrying-in port and the carrying-out port. This extends the inclined part longer than that of a flat furnace, disadvantageously upsizing the overall drying furnace.
Thus, as described in JP2008-178803 (“Patent literature 2”), a drying furnace has been developed in which a conveyance path in an intermediate part of the drying furnace is located at a high position relative to a workpiece carrying-in port and a workpiece carrying-out port and a lifting facility raises and lowers workpieces to the conveyance path.
The lifting facility used for the drying furnace of Patent literature 2 is configured such that a drop lifter in a drying booth raises and lowers a drying palette truck to an upper conveyance rail while the palette truck carries a conveyance skid for conveying an automotive body of a coating line on a roller conveyor.
However, the lifting facility of Patent literature 2 includes a strut provided outside the drying booth, the strut supporting the drop lifter (lifting apparatus) so as to raise and lower the drop lifter. Thus, a part for moving the drop lifter (lifting apparatus) in the drying booth requires a slit (clearance). This easily releases air in a high-temperature zone of the drying furnace to the outside from the slit (clearance) of the drying booth (a large heat loss in the drying booth), disadvantageously leading to low thermal efficiency in the drying furnace.
Thus, an object of the present invention is to provide a lifting facility and a conveyance system that can improve thermal efficiency in a drying furnace by preventing air in a high-temperature zone of the drying furnace from leaking to the outside.